Active matrix organic light emitting diodes (AMOLED) display becomes one of hot spots in a field of panel displays. Compared with liquid crystal displays (LCD), organic light emitting diodes (OLED) panel has advantages, such as, a lower power consumption, a lower cost, be capable of self-luminous, a broader view, a faster response and the like. Currently, conventional LCD displays in the display field such as mobile phones, PDAs, digital cameras and the like, have been replaced by AMOLED displays. Pixel driving is a core of AMOLED display and is of great importance.
Differently from a thin film transistor-liquid crystal display (TFT-LCD) which controls brightness by a stable current, the AMOLED is driven by a current, and thus needs a stable current to control light emission. As shown in FIG. 1, a conventional AMOLED pixel driving circuit may use a 2T1C pixel driving circuit. The circuit only comprises one driving thin film transistor T1, one switch thin film transistor T2 and a storage capacitor C. When a scanning line select (i.e. scan) a row, a scanning signal Vscan is at a high level. Thus, T2 is turned on and a data signal Vdata is written into the storage capacitor C. When the scanning of the row is completed, Vscan is turned into a low level signal, and T2 is turned off. T1 is driven by a gate voltage stored on the storage capacitor C, and will generate a current to drive the AMOLED. Thus, the AMOLED can emit light during a displaying of a frame continuously. The current of the driving thin film transistor T1 in a saturated state can be represented by: Ioled=K(Vgs−Vth)^2, wherein K is a parameter related with the process and design of T1, Vgs is a gate-source voltage of the driving thin film transistor, and Vth is a threshold voltage of the driving thin film transistor. Once the size and process of the transistor is determined, the parameter K is determined. FIG. 2 is an operation timing diagram of the pixel driving circuit of FIG. 1, and shows a relationship in timing between the scanning signal provided by the scanning line and the data signal provided by the data line.
The light emission of the AMOLED is caused by the current generated when the driving thin film transistor (DTFT) is in a saturated state, irrespective of using a low temperature poly silicon (LTPS) process or a oxide process. Due to an unevenness of the process, threshold voltage difference at different locations of the driving thin film transistor may be generated, which will influence the consistency of the current driving device greatly. When inputting a same driving voltage, different threshold voltages will generate different driving currents, thereby leading to an inconsistency of the current passing through the OLED. This will further cause an unevenness brightness of the display, thereby affecting the displaying of a whole image.
Thus, there is a need for a method which can improve a consistency for driving currents of driving transistors so as to improve the display quality.